EXOSAT

EXOSAT was a 1980s space X-ray telescope operated by the European Space Agency. (It has no relation to exosatellites.) It used lunar occultation observations to add precision to its observations, having been placed in a highly eccentric orbit to assist in this and to reach far enough from Earth that X-rays are unimpeded. Its surveys included a slew survey, its new discoveries designated by the prefix EXO.